Recently it was discovered that polyurethane foams contain aromatic amines. Recent evidence has also tended to indicate that certain aromatic amines may represent a potential health hazard. Although the theory of formation of the aromatic amines is not clearly understood, it appears that aromatic isocyanates and possibly their reaction products containing urea and urethane linkages are hydrolyzed to produce free aromatic amines which can be leached from the polyurethane foam. On the other hand, hindered aliphatic isocyanates due to their low reaction rate do not compete successfully with the aromatic isocyanate for functional groups during the polymerization reaction. Therefore, the hindered aliphatic isocyanate scavenger survives polymerization and is thus capable of forming urea addition products with aromatic amines as these are produced.
Applicants are aware of certain prior art believed to to be relevant. Specifically, British Pat. No. 1,368,625 describes preparation of polyurethane foams wherein from 1 to 20% by weight of an aliphatic polyisocyanate is employed in combination with conventional polyurethane foam reagents. The function of the aliphatic polyisocyanate appears to be to enhance formation of a dense integral skin during molding of the polyurethane foam. The aliphatic isocyanate is also said to contribute greatly to non-yellowing of the foam.
U.S. Pat. No. 3,790,508 describes light-stable polyurethane foams prepared by reacting a polyol, an aliphatic isocyanate, an aromatic isocyanate, a blowing agent and a catalyst. The aliphatic isocyanate index employed is from about 5 to about 40.
British Pat. No. 1,323,955 also describes formulations containing a mixture of aromatic and aliphatic isocyanates, water and a catalyst to cause trimerization of the aromatic isocyanate. The resulting foams are said to possess good physical properties as well as flame-resistance.
Applicants are further aware of the following patents:
______________________________________ U.S. Pat. No. 3,839,491 U.S. Pat. No. 3,554,962 U.S. Pat. No. 3,925,319 French 2,000,741 U.S. Pat. No. 3,590,002 German 22 34 507 U.S. Pat. No. 3,919,173 South African Pat. Publ. 68/00476 U.S. Pat. No. 3,706,710 ______________________________________